Efficient self cooling heat exchanger

ABSTRACT

An inexpensive heat exchanger is disclosed, wherein the heat exchanger is made up of a plurality of plates and each plate has at least one channel defined in the plate. The plates are stacked and bonded together to form a block having conduits for carrying at least one fluid and where the exchanger includes an expansion device enclosed within the unit. The plates include construction to thermally insulate the sections of the heat exchanger to control the heat flow within the heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of prior copending U.S. application Ser.No. 12/485,311, filed Jun. 16, 2009, the contents of which are herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the cooling of fluids through theself-cooling from the fluid. More particularly this invention goes tothe cooling of a fluid to self-cool the fluid and to cool and,potentially, liquefy another fluid.

BACKGROUND OF THE INVENTION

The demands for natural gas have increased in recent years. Thetransport of natural gas is through pipelines or through thetransportation on ships. Many areas where natural gas is located areremote in the sense that there are no convenient pipelines to readilytransfer the natural gas to the market. Therefore natural gas isfrequently transported by ship. The transport of natural gas on shipsrequires a means to reduce the volume and one method of reducing thevolume is to liquefy the natural gas. The process of liquefactionrequires cooling the gas to very low temperatures. There are severalknown methods of liquefying natural gas as can be found in U.S. Pat.Nos. 6,367,286; 6,564,578; 6,742,358; 6,763,680; and 6,886,362.

One of the methods is a cascade method using a number of shell and tubeheat exchangers. Each of these shell and tube heat exchangers, is verylarge and very expensive, and presents problems of economics andfeasibility for remote and smaller natural gas fields. It would bedesirable to have a device for liquefying natural gas that is compactand relatively inexpensive to ship and use in remote locations,especially for natural gas fields found under the ocean floor, wherecollection and liquefaction of the natural gas can be performed on boarda floating platform using a compact unit.

The most common commercial design of a heat exchanger for the cooling ofnatural gas is a spiral wound heat exchanger where the coolant cascadeswithin a shell over spiral wound tubes carrying the gas to be cooled.

There is also an increasing demand for methods of cooling gases tocondense them for transport or for separation purposes. Improvementsover the current commercial design can include lower cost, lower weight,and provide a more compact structure as well as provide improved heattransfer characteristics.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a heat exchanger made up of one or moreplates where each plate has at least one channel etched, milled,pressed, inflated, or otherwise formed in the plate. The channels eachhave an inlet and an outlet for admitting and withdrawing a coolingfluid. The channels each have an expansion device positioned within thechannel, where the coolant is expanded and provides self-cooling for thecoolant. The plates in the heat exchanger are bonded to form a coolingblock, and can be used as a heat sink for devices external to the heatexchanger. The invention is designed to improve the efficiency of theheat exchanger, and includes channels for controlling the heat flowthrough the heat exchanger. One area for controlling the heat flow islimiting the heat flow from the area for heat exchange to the area forexpanding the coolant. The heat flow is limited by providing insulatingchannels to divide regions of the heat exchanger plates. In particular,at least one insulating channel is disposed between the area for heatexchange and the area for expanding the fluid. The insulating channelscan provide separation of large sections of the plates, or can controlheat flow in smaller sections of the heat exchanger. In a second area,the channels carrying the coolant and fluid to be cooled can be designedto form a sinuous path within the plates. The paths can fold and formregions where sections of the same channel are substantially parallel,providing for undesirable heat transfer between sections of the channel.The invention includes insulating channels to thermally separatesections of the same channel, and, as such, improve the efficiency ofthe heat exchanger.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art from the following detaileddescription and drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a first embodiment showing the insulatingchannels around the expansion path;

FIG. 2 is a schematic of a portion of the heat exchanger showing thefirst and second plates, and the insulating channels proximate to theexpansion section of the first channel;

FIG. 3 is a schematic of the two plate design showing insulatingchannels; and

FIG. 4 is a schematic of one plate of the invention showing alternatepositioning of the insulating channels.

DETAILED DESCRIPTION OF THE INVENTION

The use of liquefied natural gas (LNG) is increasing, as fuel and ameans of transporting natural gas from remote sites having natural gas,without a nearby gas pipeline, to more distant areas where the naturalgas is consumed. Natural gas is typically recovered from gas wells thathave been drilled and is in the gas phase at high pressure. The highpressure gas is then treated and passed to a pipeline for transport.However, there are an increasing number of natural gas fields that arein remote locations relative to natural gas pipelines. The presentinvention is directed to a heat exchanger for cooling the natural gas atthe gas wells. By providing an inexpensive heat exchanger for coolingand liquefying natural gas in remote locations, natural gas can berecovered on site and transported as LNG, rather than requiring anatural gas pipeline, or transporting the gas at very high pressures. Inaddition, the present invention can be used as a means for cooling othermaterials, such as providing for a cooling device to cool electronics orother devices that generate heat and need external cooling.

The efficiency of the heat exchanger is affected by the heat transfer tothe expansion device where a substantially adiabatic expansion isaffected. The present invention is designed to reduce the undesirableheat flow from the heat transfer region to the expansion region of theheat exchanger. The creation of a barrier region to limit heat flow tothe expansion region improves the thermodynamic efficiency of theexpansion of the cooling fluid.

The plates have channels etched, milled, pressed, stamped, inflated, orby other methods known in the art, into them for the transport ofcoolant and fluid to be cooled. When the plates are bonded together, thechannels are covered and form conduits through which fluids can flow.The bonding method will depend on the materials of construction, such aswith aluminum plates, bonding involves brazing the aluminum platestogether. With steel, diffusion bonding or welding can be performed tobond the steel plates together. Other means of bonding plates are knownto those skilled in the art.

The present invention presents a thermal barrier to limit the amount ofheat flowing from the heat exchange section of the heat exchanger to theexpansion section of the heat exchanger. The present invention, as shownin FIG. 1, is a heat exchanger that includes at least one first plate10. The plate 10 has a first channel 12 defined therein having an inlet14 and an outlet 16. The first channel 12 has three sections: a firstsection for carrying a cooling fluid, a second section having anexpansion device where the cooling fluid is expanded, and a thirdsection for carrying the expanded cooling fluid. The cooling fluid canalso be termed a coolant or refrigerant. The heat exchanger plate hastwo regions, a heat exchange region which encompasses the first secondof the first channel 12 and the third section of the first channel 12,and an expansion section which encompasses the second section of thefirst channel 12. The second section of the first channel 12 includes anexpansion device 18 positioned within the second section of the channel.The first plate 10 also includes at least one insulating channel, butpreferable a pair of insulating channels 22, 24. When there is a singleinsulating channel 22, the insulating channel is disposed between thesecond section of the first channel 12 and the heat exchange region ofthe plate 10. The insulating channels 22, 24 are defined in the plate 10along a path that is substantially parallel to the second section of thefirst channel 12, and the insulating channels 22, 24 are in fluidisolation from the first channel 12. The heat exchanger includes a coverplate 30 to cover the channel 12 in the upper most plate 10 of a stackof plates.

The first plate 10 can be divided into two sections: a heat exchangesection 40, and an expansion section 48. The insulating channels 22, 24would be disposed in the expansion section 48, and the heat exchangesection 40 is where heat transfer from a fluid being cooled to theexpanded fluid takes place. In the heat exchange section 40, the thirdsection of the first channel 12 is preferably substantially parallel tothe first section of the first channel 12 to provide self-cooling of theincoming coolant.

The insulating channels 22, 24 can include an access port 32 to allowfor external gas flow through the insulating channels 22, 24, or toallow for the injection of an insulating material into the channels 22,24. For multiple plates 10, the insulating channels can include anopening 26 that passes through the plate 10. Other designs can includedifferent paths for providing access to the insulating channels 22, 24.The insulating channels 22, 24 can be filled with a low conductivitygas, or an insulating material having a thermal conductivity of lessthan 0.1 W/m-K. Insulating materials can be chosen for the expectedoperational temperature ranges. Examples of insulating materials includeperlite, cellular glass insulation, polyurethane insulation,polyisocyanurate insulation, fiberglass, polystyrene, and elastomericfoams. Some of these insulating materials are appropriate fortemperatures near or below cryogenic temperature ranges, such as totemperatures as low as −260° C. The inner insulation channel 22 can beenlarged to comprise a hole that extends through the plate 10, providinga larger volume of low conductivity. Likewise, with other insulatingchannels, when the design allows for the insulating channels to beenlarged and extended through each plate, the insulating channels cancomprise holes within the plates.

The heat exchanger can include a manifold 70 having a manifold firstinlet channel 74 in fluid communication with each first channel inlet14, and a manifold first outlet channel 76 in fluid communication witheach first channel outlet 16.

The heat exchanger can include a second channel 42 defined within theplate 10. The second channel 42 includes a second channel inlet 44 and asecond channel outlet 46 for carrying a fluid to be cooled, and thesecond channel 42 is in fluid isolation from the first channel 12. Themanifold 70 for carrying fluid to the heat exchanger can include amanifold second inlet channel 78 in fluid communication with each secondchannel inlet 44 and a manifold second outlet channel in fluidcommunication with each second channel outlet 46. Variations on themanifolds 70 include multiple manifolds, where each manifold used has asingle channel to either distribute or collect fluids to and from theheat exchanger. Other variations include single manifolds per side ofthe heat exchanger, where each manifold has the appropriate number ofchannels for the side the manifold is mounted on the heat exchanger.

In one embodiment, the invention comprises a heat exchanger as describedabove, but with at least one second plate, and where the first andsecond plates are stacked in an alternating manner. The second plate hasan insulating channel formed therein, where the second plate insulatingchannel is positioned under the expansion section of the first channel.This can be seen in FIG. 2, where the Figure shows a section of the heatexchanger. The section shows a first plate 10 with the expansion sectionof the first channel 12 and two insulating channels 22, 24 on eitherside of the expansion section of the first channel 12. The plates arestacked such that the second plate 50 is positioned below the firstplate 10, and has a second plate insulating channel 52, and where thesecond plate insulating channel 52 is disposed below the first channel12 expansion section. The second plate insulating channel 52 limits theamount of heat flow from the second plate through the heat exchangesection. When the invention comprises multiple first 10 and second 50plates, the expansion section of the first channel 12 has an insulatingchannel 52 above it and below it, as well as insulating channels 22 and24 on either side. The width of the channel 52 in the second plate 50 ispreferably greater than the width of the first channel 12 in the firstplate 10. This provides more insulating capability for restricting theheat flow from the second plate 50 to the expansion region of the firstplate 10. The insulating channel 52 in the second plate 50 can be filledwith a low conductivity gas, or filled with an insulating materialhaving a conductivity less than 0.1 W/m-K. An access channel can bedefined in the second plate 50 in fluid communication with theinsulating channel 52, for providing a means for filling the insulatingchannel 52 with an insulating material after the assembly of the heatexchanger. Examples of insulation materials are listed above, and thechoice is dependent on the operational range of the heat exchanger.

The heat exchanger having pairs of first 10 and second 50 plates allowsfor a second fluid channel 54 in the second plate for carrying a fluidto be cooled, as shown in FIG. 3. In an alternate embodiment, the heatexchanger comprises a first plate 10 for carrying the coolant in a firstchannel 12. The coolant passes through the expansion section 48 of theplate 10 and is passed back to the heat exchange section 40. Theexpansion section 48 is insulated by insulating channels 22 and 24 inthe first plate 10. The second plate 50 includes a second channel 54 forcarrying a fluid to be cooled, where the second channel has an inlet 53and an outlet 56. The second plate includes an insulating channel 52disposed proximate to the section of the first channel 12 after thecoolant is expanded. The insulating channels are in fluid isolation fromthe channels carrying coolant and fluid to be cooled. The insulatingchannels can include access ports 28, 58 to the exterior of the heatexchanger when the exchanger is assembled.

The second channel 54 follows a substantially parallel path to the thirdsection of the first channel 12. The insulating channel 52 provides abarrier to heat flow from the cooled fluid to the expansion region 48 ofthe first plate 10.

In an alternative to a manifold for the distribution and collection offluid streams to and from the heat exchanger, the heat exchanger coverplate 30 can include a first channel inlet port in fluid communicationwith each first channel inlet 14, and a first channel outlet port influid communication with each first channel outlet 16. With thisembodiment, in an alternative to terminating at the edge of a plate, thefirst channel inlets 14 pass through each plate 10 and are in fluidcommunication with the cover plate first channel inlet port. Likewise,the first channel outlets 16 pass through each plate 10 and are in fluidcommunication with the cover plate channel first channel outlet port.With this embodiment, the cover plate 30 can include second channelinlet ports in fluid communication with each second channel inlet 44 andsecond channel outlet ports in fluid communication with each secondchannel outlet 46, where each second channel inlet and outlet, insteadof terminating at an edge of a plate 10 pass through each plate 10.

The insulating channels can also be positioned to provide thermalseparation of neighboring sections of any channels to limit thermalcommunication. The insulating channels can improve the effectiveness ofthe heat exchange zone between two neighboring channels by thermallyisolating sections that fold in a sinuous pattern. An example of thefurther use of insulating channels is shown in FIG. 4. The heatexchanger comprises at least one plate 10 having a first channel 12defined therein, and having an inlet 14 and an outlet 16. The plate 10can be divided into two sections, a heat exchange section 40 and anexpansion section 48, where the expansion section 48 is partiallythermally insulated from the heat exchange section 40 by an insulatingchannel, or by an insulating region, such as a hole 60 through the plate10. The hole 60 can be filled with a low conductivity gas, or aninsulating material.

The first channel 12 follows a sinuous path, where there is a firstsection for carrying a coolant. The first channel 12 then passes througha second section that is disposed within the expansion section 48 of theplate 10. The first channel 12 continues back to the heat exchangesection 40 where the first channel 12 follows a sinuous path to providea longer heat exchange path for the coolant. The sinuous path of thefirst channel 12 folds back on itself, and is separated by a insulatingchannel 62 to limit the heat flow between neighboring sections of thefirst channel 12. The first channel 12 can include an insulating channel24 that is substantially parallel to the first channel 12 in theexpansion region 48 around the section including an expansion device 18.

The plate 10 can further include a second channel 42 defined therein,and having an inlet 44 and an outlet 46. In one design, the secondchannel 42 follows a path that is substantially parallel to the thirdsection of the first channel 12 in the heat exchange section 40 of theplate. The sinuous path has the second channel 42 folding back onitself, and to prevent heat transfer between neighboring portions of thesecond channel 42, insulating channels 64 are defined in the plate 10.

In an alternate design, the heat exchanger can further include at leastone second plate 50, where the first 10 and second plates 50 are stackedin an alternating arrangement. In the alternate design, the secondchannel 42 is disposed on the second plate 50, instead of the firstplate 10. The second channel 42 can follow a substantially parallel pathto the first channel 12 in the first plate 10, and the sections of thefirst 12 and second 42 channels that fold back upon themselves can beseparated by insulating channels.

The present invention can comprise complex geometric arrays of channelsfor cooling a fluid, where there are additional insulating channels toreduce cross heating of channels when undesired. Upon reading thisdescription, one skilled in the art can contemplate many geometricarrays that fall within the scope of the invention. This insulatingchannel invention is intended to apply to heat exchanger designs thatalso do not include an expansion device within the exchanger.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications and equivalent arrangementsincluded within the scope of the appended claims.

The invention claimed is:
 1. A heat exchanger comprising: at least onefirst plate having a first channel defined therein having an inlet andan outlet, wherein the first channel is defined by a first section forcarrying a cooling fluid, a second section where the fluid is expanded,and a third section carrying the expanded fluid, wherein the first andthird section of the first channel are in a heat exchange region and thesecond section of the first channel is in an expansion region, and atleast one insulating channel, wherein the insulating channel follows apath substantially parallel to the second section of the first channel,the insulating channel is disposed between the second section of thefirst channel and the heat exchange region; a second channel defined inthe at least one plate having a second channel inlet and a secondchannel outlet, wherein the second channel is in fluid isolation fromthe first channel, and is substantially parallel to the third section ofthe first channel, wherein the third section of the first channelprovides cooling to both the first section of the first channel and thesecond channel; an expansion device disposed within the second sectionof the first channel; and a cover plate.
 2. The heat exchanger of claim1 further comprising at least one manifold having a manifold first inletchannel in fluid communication with each first channel inlet, a manifoldfirst outlet channel in fluid communication with each first channeloutlet, a manifold second inlet channel in fluid communication with eachsecond channel inlet, and a manifold second outlet channel in fluidcommunication with each second channel outlet.
 3. The heat exchanger ofclaim 1 further comprising a second channel inlet port defined in thecover plate and is in fluid communication with the second channel inletand a second channel outlet port defined in the cover plate and in fluidcommunication with the second channel outlet.